<span>3) which is an example of a physical change
</span><span>a) grinding pepper</span>
<u>Answer:</u>
<u>For a:</u> The wavelength of light is 
<u>For b:</u> The light is getting absorbed
<u>Explanation:</u>
To calculate the wavelength of light, we use Rydberg's Equation:

Where,
= Wavelength of radiation
= Rydberg's Constant = 
= Higher energy level = 7
= Lower energy level = 3
Putting the values in above equation, we get:

Hence, the wavelength of light is 
There are two ways in which electrons can transition between energy levels:
- <u>Absorption spectra:</u> This type of spectra is seen when an electron jumps from lower energy level to higher energy level. In this process, energy is absorbed.
- <u>Emission spectra:</u> This type of spectra is seen when an electron jumps from higher energy level to lower energy level. In this process, energy is released in the form of photons.
As, the electron jumps from lower energy level to higher energy level. The wavelength is getting absorbed.
Answer:
ΔH = -20kJ
Explanation:
The enthalpy of formation of a compound is defined as the change of enthalpy during the formation of 1 mole of the substance from its constituent elements. For H₂S(g) the reaction that describes this process is:
H₂(g) + S(g) → H₂S(g)
Using Hess's law, it is possible to sum the enthalpies of several reactions to obtain the change in enthalpy of a particular reaction thus:
<em>(1) </em>H₂S(g) + ³/₂O₂(g) → SO₂(g) + H₂O(g) ΔH = -519 kJ
<em>(2) </em>H₂(g) + ¹/₂O₂(g) → H₂O(g) ΔH = -242 kJ
<em>(3) </em>S(g) + O₂(g) → SO₂(g) ΔH = -297 kJ
The sum of -(1) + (2) + (3) gives:
<em>-(1) </em>SO₂(g) + H₂O(g) → H₂S(g) + ³/₂O₂(g) ΔH = +519 kJ
<em>(2) </em>H₂(g) + ¹/₂O₂(g) → H₂O(g) ΔH = -242 kJ
<em>(3) </em>S(g) + O₂(g) → SO₂(g) ΔH = -297 kJ
<em>-(1) + (2) + (3): </em><em>H₂(g) + S(g) → H₂S(g) </em>
<em>ΔH =</em> +519kJ - 242kJ - 297kJ = <em>-20 kJ</em>
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I hope it helps!
The answer is C.
The vast difference in electronegativity of the oxygen and hydrogen in water, the O-H bond is polar.